The present invention relates to a flywheel structure of an outboard motor.
In an engine of, for example, an outboard motor, an ignition plug generates spark to ignite air-fuel mixture in a cylinder to burn the mixture. This combustion in the engine is closely related to the ignition timing of the ignition plug, and in order to burn the mixture efficiently, it is necessary to appropriately set the ignition timing.
In the engine, a speed of a piston is increased as the engine revolution number is increased, and thus, it is common to set the ignition timing faster as the engine revolution number is increased.
An apparatus for automatically advancing the ignition timing in accordance with increase in the engine revolution number is called an automatic (spark) advance system (automatic timer). Conventionally, a mechanical automatic advance system utilizing a difference in centrifugal force caused by revolution of the engine has been used in many cases. Recently, in order to set more appropriate the ignition timing, there has been used an electronic automatic advance system utilizing the revolution number and revolution angle of the engine (crankshaft), opening degree of a throttle and the like as parameters to set the ignition timing that is more suitable for a driving state by means of a microcomputer.
In the case of an engine mounted in the outboard motor, in which a crankshaft is disposed perpendicularly, the revolution number and a revolution angle of the crankshaft are obtained by detecting, by using a detection sensor or the like, a motion of the detection member such as a trigger pole or the like provided on a flywheel provided on an upper end of the crankshaft so that they are rotated in unison (e.g., see Japanese Patent Laid-open Publication No. HEI 10-22026).
In a known structure, the trigger pole projects from an outer peripheral surface of the flywheel diametrically outward of the flywheel, and the detection sensor is disposed outside the trigger pole.
When the crankshaft also functions as a driving shaft for a camshaft, the detecting member is disposed below a drive pulley around which a timing belt is wound or the detecting member is disposed between the flywheel and the drive pulley.
The flywheel is provided with a magneto or a ring gear that is operatively connected to a drive gear of a starter motor so as to be rotatable in unison.
However, in the case of an engine in which a flywheel is provided with a ring gear, if a trigger pole, as a detecting member, projects from the outer peripheral surface of the flywheel, the detection sensor and the ring gear disposed outside the trigger pole may adversely interfere with each other. Therefore, the ring gear must consequentially be disposed at a higher position. As a result, a position of the center of gravity of the engine becomes higher, vibration of the crankshaft is increased, and there is an adverse possibility that durability of the crankshaft and its bearing may be lowered.
Further, in the case of an engine in which the detecting member is disposed below the drive pulley or between the flywheel and the drive pulley, a special procedure may be necessary for guiding the timing belt, or the diameter of the detecting member is reduced and the precision of the position (angle) of the detecting member is lowered. Furthermore, since the diameter of the detecting member is reduced, the starting revolution number (controllable revolution number) of the engine is increased, and the starting performance is deteriorated.
In the case of an engine having a flywheel provided with a magneto, the magneto and the engine are heated to increase a temperature around the engine, which speeds up deterioration of an electrical equipment disposed therearound. Further, a wire used for a stator coil of the magneto must have high heat resistance, which will increase costs.
The present invention has been accomplished in view of the above-described circumstances, and it is an object of the present invention to provide a flywheel structure of an outboard motor capable of lowering the center of gravity of an engine and enhancing the starting performance of the engine.
It is another object of the present invention to provide a flywheel structure of an outboard motor capable of facilitating the cooling operation around the flywheel.
These and other objects can be achieved according to the present invention by providing a flywheel structure of an outboard motor in which a crankshaft is disposed perpendicularly in an engine, a flywheel is disposed to an upper end portion of the crankshaft to be rotatable in unison with the crankshaft and the flywheel is provided with a detecting member a motion of which is detected by a sensor means to thereby detect the number of revolution and a revolution angle of the crankshaft, wherein the detecting member is disposed in an axial direction of the crankshaft.
In a preferred embodiment, the detecting member is arranged on a lower surface of the flywheel along a circumferential direction thereof, the detecting member is formed, at an outer end thereof, with a centrifugal fan-shaped portion for discharging an air inside of the detecting member to an outside thereof when the flywheel is rotated.
The flywheel is provided at, an outer peripheral edge portion thereof, with a ring gear for starting an engine, the detecting member and the sensor means are disposed inside of an outer diameter of the ring gear in a plan view.
Three or more numbers of the detecting members are arranged on the lower surface of the flywheel at an equal distance from one another in the circumferential direction thereof, a notch is formed to each of the detecting members by removing a portion thereof.
The flywheel is provided, at an upper surface thereof, with a fan member for introducing an air outside the flywheel into the flywheel.
The detecting member has a size K in a diametrical direction thereof, which is set to be equal to or greater than a size S of the detecting member in the circumferential direction thereof.
The detecting member is a trigger pole projecting downward towards the engine and the sensor means comprises a pulser coil disposed to the engine.
As explained hereinabove, according to the present invention, in a flywheel structure of an outboard motor for detecting, by using a sensor means, a motion of a detecting member provided on a flywheel which is formed on an upper end of a crankshaft so that the flywheel is rotated in unison with the crankshaft, thereby detecting the number of revolution and a revolution angle of the crankshaft, and the detecting member is disposed in an axial direction of the crankshaft. Therefore, the position of the ring gear can be set lower, and the position of the center of gravity of the engine can be lowered.
The detecting member is disposed on a lower surface of the flywheel in its circumferential direction, the detecting member is formed at its outer end with a centrifugal fan-shaped portion for discharging the air inside the detecting member to the outside of the detecting member when the flywheel is rotated. Therefore, the space surrounded by the flywheel and the engine can be cooled efficiently with a simple structure.
Further, the flywheel is provided, at its outer peripheral edge, with a ring gear for starting an engine, the detecting member and the sensor means are disposed inside of an outer diameter of the ring gear as viewed from above. Therefore, the layout can be made compact.
Furthermore, the number of the detecting member is three or more, which are disposed on the lower surface of the flywheel at at equal distance from one another in its circumferential direction, and a notch is formed on each of the detecting members by removing a portion thereof. Therefore, wind noise generated by the detecting means at a time when the flywheel is rotated can be reduced.
Furthermore, the flywheel is provided at its upper surface with a fan structure for introducing air outside the flywheel into the flywheel. Therefore, the space surrounded by the flywheel and the engine can be cooled efficiently with a simple structure.
Further, a size of each of the detecting members in its diametrical direction is set to be equal to or greater than a size of the detecting member in its circumferential direction. Therefore, cranking noise generated when the engine is started is reduced.
The nature and further characteristic features of the present invention will be made clear from the following descriptions made with reference to the accompanying drawings.